Influence Of Beam Quality On Propagation And Focus Of Laser Beam And Quality Of Laser Materials Processing

Research, development, application and industrialization of modern laser manufacturing technology play an important role on the development of National Economy. High power and high beam quality are the basic requirements for light source in the field of laser manufacturing. The start of researching on laser technology in our country is earlier, but more attention is concentrated on high power, the beam quality is ignored. In fact, laser beam quality is a main parameter that has key action on laser materials processing from the beginning to the end. In this dissertation, the parameter used to evaluate laser beam quality is proposed. The influence of beam quality on beam propagation and focus are studied in theory and measurements separately. Finally, takes laser penetration welding as a sample, the effect of beam quality on laser processing is discussed.Based on analyse of parameters which used to evaluate laser beam quality at present and according to the main properties which influence on laser manufacturing, beam focus characteristics parameter is put forward as the stander parameter to evaluate beam quality, because the foundmental advantage of laser beam applied in industral field is that laser beam can achieve high energy intensity through focusing. The practical meaning of lies in two aspects. On one hand, is the product of beam waist radius and half divergence angle, wavelength is not involved. So there is possibility to compare the acutal focusing ability among laser beams with different wavelength. On the other hand, is a calculated result by measuring experiment, and it is more brief and persuadable than M 2factor, since the latter one is a ratio with basic mode Gauss beam.Imaging formula and object-image scale formula of laser beam transferred by focus lens are deduced according to the ABCD law of matrix optics, and the factors that effect on beam focus properties are analyzed based on these two formulas. The results show that radius and position of focal beam waist, focal angle and focal depth describe focal beam properties. They are determined by waist and Rayleigh length of beam before focusing, the position and focal length of focus mirror. So, it is clear that the beam quality and focusing system determine the focal beam properties together, K fand Fnumber describe them separately. Laser beam quality influences on beam...